Crankcase Evacuation Systems

What Is a Crankcase Evacuation System?

A crankcase evacuation system removes blow-by gases, moisture and pressure from your engine's crankcase. That lets the internals run under a slight, controlled vacuum instead of positive pressure. As your pistons move, combustion pressure slips past the rings and into the crankcase.

That blow-by carries fuel, water vapor and contaminants that dilute your oil and drive crankcase pressure up. Left unchecked, that pressure looks for a way out, and it usually finds your weakest gasket or seal. An evacuation system gives those gases a controlled exit and replaces positive pressure with vacuum.

You'll see the category cover simple valve cover breathers, larger catch cans and complete weld-on setups with a vacuum pump. If you're mapping out a full oil system refresh, it pairs naturally with the rest of your oil system parts.

Not sure where to start? Shop All Crankcase Evacuation Systems and match the setup to your engine and budget.

How Does a Crankcase Evacuation System Work?

Every crankcase evacuation system does the same job, pulling air out of the crankcase, but there are two common ways to get there. Exhaust-scavenged systems tap into your headers with weld-in bungs and a check valve on each side.

As exhaust flows past those fittings, it creates a low-pressure zone that draws crankcase gases into the stream. The check valves stop exhaust from backing up into the engine. This method is simple, affordable and popular on drag and circle-track cars that spend time at wide-open throttle.

The other approach uses a crankcase vacuum pump. An electric crankcase vacuum pump or a belt-driven mechanical pump actively pulls a measurable, adjustable vacuum no matter what the throttle is doing. That makes it the choice for high-horsepower and forced-induction builds.

Want the details on sizing and mounting a pump? Read our beginner's guide to vacuum pumps before you buy. Match the method to how and where you drive.

Benefits of Running Crankcase Vacuum

Pulling a vacuum on the crankcase does more than tidy up your engine bay. Lower pressure changes how the bottom end behaves, and the payoffs stack up on the street or the strip. Here's what running crankcase vacuum can do for your engine:

• Improves piston ring seal, since lower crankcase pressure lets the rings sit tighter against the cylinder walls.
• Reduces blow-by by giving combustion gases a clear path out instead of pooling below the pistons.
• Cuts oil leaks and gasket failures, because there's no positive pressure pushing oil past your seals.
• Improves ring and cylinder lubrication, helping the oil your oil pumps and pickups deliver stay where it belongs.
• Removes moisture and fuel vapor that would otherwise dilute your oil and shorten its life.
• Frees up potential horsepower, since reduced windage and better ring seal cut parasitic drag.

Crankcase Evacuation System Components

Once you know the approach you want, you'll build the system from a handful of parts. Breathers are the starting point. A valve cover breather or crankcase breather filter vents the engine and blocks debris.

An oil breather cap does the same job in a compact package. To keep oil mist out of your intake, add an oil catch can or an air/oil separator, which trap vapor and let clean air pass. Browse dedicated oil catch cans and breather tanks if you want a larger reservoir for a boosted or high-rpm engine.

Exhaust-scavenged builds rely on check valves, weld-on fittings and hoses to route everything safely. A vacuum-pump build adds the pump plus a mounting bracket. Serious race combinations often build evacuation into dry sump systems for maximum control over crankcase pressure.

Popular parts here come from Moroso, Mishimoto, Vibrant Performance, JAZ Products, Mr Gasket and B&B. For build tips and install walkthroughs, browse our engines and components tech articles.

How Much Does a Crankcase Evacuation Kit Cost?

How much you spend on a crankcase evacuation kit comes down to the method you choose and how much hardware it includes. A single valve cover breather or breather cap can start around $15, so upgrading your venting is an inexpensive first step.

A quality oil catch can or air/oil separator kit typically runs from roughly $100 into the low hundreds, depending on capacity, materials and fittings. Complete weld-on exhaust evacuation systems with check valves and hardware sit higher in that range. Adding an electric crankcase vacuum pump pushes a full setup toward several hundred dollars.

Budget for the whole oil system, not just this category. Fresh oil pans and components or new engine dipsticks and tubes keep everything sealing and reading right. Prices and stock vary by brand and fitment, so check the current listing for your combination.

Ready to build your setup? Shop All Crankcase Evacuation Systems and filter by part type, brand and price.